A file folder containing papers from Supreme Court nominee John G. Roberts Jr.'s work on affirmative action more than 20 years ago disappeared from the Ronald Reagan Presidential Library after its review by two lawyers from the White House and the Justice Department in July, according to officials at the library and the National Archives and Records Administration.

Archivists said the lawyers returned the file but it now cannot be located. No duplicates of the folder's contents were made before the lawyers' review. Although one of the lawyers has assisted in the Archives' attempt to reconstruct its contents from other files, officials have no way of independently verifying their effort was successful.

It is rare for the Archives to lose documents in its care and the agency has requested an investigation by its inspector general, said Sharon Fawcett, the assistant archivist for presidential libraries.

The lost file has also aroused some concern on Capitol Hill. Sen. Patrick J. Leahy (Vt.), the senior Democrat on the Judiciary Committee, wrote yesterday to R. Duke Blackwood, executive director of the Reagan Library, asking that he "continue to investigate thoroughly" the missing affirmative action file and "clarify the basis upon which you believe you have reconstructed that file." And Sen. Edward M. Kennedy (D-Mass.) requested a Justice Department investigation because one of the agency's lawyers had seen the documents involved.

At issue is one of hundreds of files maintained by the Reagan Library in Simi Valley, Calif., where an estimated 55,000 pages of material from Roberts's tenure as White House associate counsel from 1982 to 1986 are archived. The library is managed by the Archives.

As part of a vetting process before Roberts's formal nomination by the White House in late July, the two lawyers requested and were granted special access to the Roberts files. Neither the White House nor the Justice Department would name the lawyers yesterday, but sources said one works for White House counsel Harriet Miers and the other is an aide to Attorney General Alberto R. Gonzales.

Upon the lawyers' arrival, Archives officials said, they asked to inspect various folders, and as they were pulled from the boxes, a marker was inserted in their place and the lawyers signed a checkout sheet. An attendant present in the room at all times did not, as a matter of routine, sign a form signifying the return of each folder.

Nonetheless, Fawcett said, "we are quite confident that the records were returned to us." Asked why, she said that while the attendant does not recall seeing the affirmative action file in question put back, the marker was not in the box after the lawyers departed. "It would have been very difficult, given the circumstances in the room," for the lawyers to have retained the file because they were separated from their bags, she said.

Instead, the folder was evidently lost later when all of the Roberts documents were transferred to new, acid-free folders and reorganized in anticipation of their disclosure to the Senate and news media.

It is "very difficult to believe it's anyone other than ourselves responsible for this loss," Fawcett said.

Officials said they believe the file included a memo from Roberts urging the White House to withhold any response to two church officials who complained about the administration's policies on affirmative action in the workplace. "The debate is still raging" about proposed changes that would eliminate affirmative action goals and timetables, Roberts wrote, so "I recommend closing them out with no response," according to a copy of the memo provided by the administration yesterday.

White House spokesman Steve Schmidt said that notes taken by the Justice Department lawyer provided the archivists "with the road map to reconstruct the file." He praised the library for doing a job that "normally would have taken three months in three weeks," sorting through tens of thousands of pages of documents and making them available as quickly as possible.

"Hopefully that missing folder will turn up at the library," he said. "But what's most important is for people to understand the remarkable job that the staff at the Reagan Library did."